As a technology related to a storage apparatus, an external storage connection technology for connecting an external storage apparatus to an internal storage apparatus, which receives a request from a host, and for providing a logical volume, which exists in the external storage apparatus, to the host via the internal storage apparatus is known (refer to Patent Literature 1). In the external storage connection technology, when an I/O (Input/Output) request with respect to a logical volume has been received from the host, the internal storage apparatus determines whether the access-target logical volume is a logical volume, which exists in the internal storage apparatus, or a logical volume, which exists in the external storage apparatus, and based on the result of the determination, assigns the I/O request to the storage apparatus in which the access-target logical volume exists.
Furthermore, as a technology related to a storage apparatus, a volume migration technology for migrating data in a migration-source logical volume to a migration-destination logical volume in a state in which an I/O request from a host application can be processed as-is known (refer to Patent Literature 1). In the volume migration technology, the data of the migration-source logical volume is copied to the migration-destination logical volume, and configuration control information is configured for the migration-destination logical volume. The migration-source logical volume and the migration-destination logical volume may be logical volumes in the same storage apparatus, or may be logical volumes in different storage apparatuses.
As another technology related to a storage apparatus, a storage virtualization technology for forming a hierarchical pool using multiple types of storage devices each having a different performance, and for allocating a real storage area (hereinafter referred to as either “physical page” or “page”) registered in the hierarchical pool to a virtual volume in accordance with a write access from a host is known (refer to Patent Literature 2). In the storage virtualization technology, a virtual storage area in a virtual volume is partitioned into multiple partial areas (hereinafter referred to as “virtual segment”), and a determination is made as to the tier of the hierarchical pool from which a page is to be allocated for each virtual segment. The storage apparatus, for example, either regularly or irregularly revises the tier to which a page for allocation to a virtual segment belongs (page reallocation) based on the number of I/Os with respect to the virtual segment. For example, a page belonging to a high-performance tier formed using a high-performance storage device is allocated to a virtual segment having a large number of I/Os, and a page belonging to a low-performance tier formed using a low-performance storage device is allocated to a virtual segment having a small number of I/Os.
In addition, a technology, which combines the external storage connection technology and the storage virtualization technology, creates a virtual volume in a storage apparatus in which the external storage connection technology is being applied by using multiple types of storage devices each having a different performance to form a hierarchical pool, and revising the tier to which a page for allocation to the virtual segment belongs based on the number of I/Os to the virtual segment is known. In addition to a physical page of a storage device of an internal storage apparatus, a physical page of a storage device of an external storage apparatus can also be registered in a hierarchical pool of a storage apparatus in which the external storage connection technology is being applied.